Electrical protective system



June 9,1936. L, K, SW'ART 2,043,399

ELECTRICAL PROTEGTI VE SYSTEM Filed Feb. 20, 1935 INVENTOR ATTORNEYPatented June 9, 1936 UNITED STATES PATENT OFFICE ELECTRICAL PROTECTIVESYSTEM Application February 20, 1935, Serial No. 7,451

2 Claims.

This invention relates to electrical protective systems. Moreparticularly this invention relates to arrangements for simultaneouslygrounding a plurality of circuits when induced voltages becomeimpressed. thereon.

Protector blocks having air gaps which break down at predeterminedpotentials have recently been used in the telephone art for theprotection of telephone circuits from high voltages set up therein byone or more sources extraneous to the circuits themselves. Variousarrangements have been used to accomplish this result. Some of thearrangements employed a resistor or a saturating reactor interposed inthe ground connection of said protector blocks. The resistor or reactoras the case may he, carries all of the operating current of the blocksassociated therewith. The impedance drop across the resistor or reactoris rectified by a rectifier which generally is of the copper-oxide type.The rectified current is applied tothe winding of a relay which, whenoperated, shunts the protector blocks so that any induced current orcurrents are carried through the heavy duty contacts of the relay.

In other arrangements a saturating reactor or transformer has beenemployed to operate a common master relay which applies a local batterypotential to the windings of a multiplicity of short-circuiting relaysto cause simultaneous grounding of all conductors associated therewith.There is an advantage in eliminating the maintenance expense inconnection with the dry cell batteries frequently used on the lattertype of relay protector system, especially where these protectors arelocated in outlying districts.

It is not quite satisfactory to use rectifying apparatus of thecopper-oxide type as now generally employed in short-circuiting relayprotectors, since the characteristics of the rectifiers change rapidlywith age and are subject to wide variations due to humidity. Moreoverthese rectifiers seldom return to their original state after a severeapplication of voltage or after the passage of a large current.Furthermore, the characteristics continuously change with variations intemperature. The most serious drawback to their use lies in the narrowrange of operating current. Even with elaborate shunting arrangements,the range of operation from minimum to maximum operating current isdecidedly limited and it is relatively easy to apply voltage to thecopper-oxide rectifier discs which can exceed the safe value of thedisc. When this limit is exceeded a rupture in the surface insulation ofthe disc takes place, rendering them thereafter ineffective. All of thedescribed defects substantially affect the sensitivity of the device andreduce its range of operation, and any arrangement, therefore, dependingupon the use of cop- 5 per-oxide rectifiers is especially undesirable.

As is well known in the art, the saturating transformer can be reliedupon to hold the root mean square values of voltage to low values, eventhough the currents applied to the primary may rise to several hundredtimes the minimum operating current of a device applied to saidtransformer. However, it is known that peak voltages may be obtained onthe secondary winding of the saturating transformers for very shortperiods of time. These voltages are of steep wave front and if directlyapplied to rectifiers of the copper-oxide type, these rectifiers wouldbe almost immediately rendered ineffective due to the puncture of thesurface insulation of the rectifier discs. These steep wave frontsurges, however, could be suppressed by the use of thyrite. This becomesundesirable due to the space dimensions of the thyrite required.

By employing gas tube rectifiers of the cold cathode type thepossibility of damage (to the copper-oxide rectifiers) is greatlyremoved along with all the inherent disadvantages.

Furthermore, the gas tube devices can be made to operate only above acertain desired value of voltage. The current, therefore, passing toground through the saturating transformer or reactor can be required toexceed a certain known value before operation of the short-circuitingrelay takes place. Steep wave front voltages ob- 35 tained on thesecondary winding of the saturating transformer will not damage the gastube rectifiers. Moreover, the gas tube rectifying devices can bedesigned to have a wide margin between the breakdown value of voltageand the 40 voltage required to sustain the glow in the gas within thetube. This wide margin of Voltage renders immediately availableconsiderable energy for the operation of the short-circuiting rer lays.By employing the combination of asaturating reactor or transformer whichpermits of wide operating values of the device, with gas tubes of therectifier type and sensitive direct current relays, short-circuiting ofthe protector blocks can be accomplished at high speed for currents toground in eXcess of a certain desired value and without possibility ofdamage to the rectifier tubes and without the inherent limitations ofthe copper-oxide rectifying devices. The socalled sharply definedmarginal or trigger operation that is obtained by the use of gas tubeswhich operate at values only in excess of certain predetermined valuesprovides a decided advantage in that it does not short-circuit norground the conductors for such steep wave front short-lived impulses asare obtained from small cloud discharges or static as commonly found onopenwire telephone conductors. Only currents of magnitudes which willdamage the protector blocks would cause operation of the relayprotectors.

By employing a multiplicity of short-circuiting direct current relaysthe windings of which are connected either in series or in multiple orby employing a common inulti-contact shortcircuiting direct currentrelay, the short-circuiting of practically any number of conductors maybe accomplished with but small'amounts of power derived from theprotector blocks to ground. Short-circuiting relays even though designedto carry considerable current will operate within a few thousandthsof asecond after current is passed. across theopen spaced protector blocksand these; relays will restore to normal and removethe short circuit.from said protector blocks in a few 'thousandthsof a second afterwithdrawal of the potential between the exposed conductors and-earth.

Furthermore biasing direct current potentials maybe-used to raiseorlower the operating value of thegas-tubes and where the use of biasingpotential becomes feasibleand where this. potential isproperly poled,there-is an added advantage in its-use in that. the direct currentthrough the relay will be increased.

This invention and the principles underlying it, some-of which-have beendescribed hereinabove, will. be better understood from the descriptionhereinafter following when read in connection with theaccompanyingdrawing in which Fig. 1 represents one embodiment of. the invention andFig. 2 represents a modification of some of the apparatus shownin. Fig.1..

In Fig. 1 reference. charactersWi, W2, W3 and W4: represent four: of. aplurality of conductors to which. are connected individual open spacedprotectorblocksPi, P2,.P3 and P4, respectively. The remaining terminalsofsaid protector blocks are multipled together andconnectedto theprimary winding of; a. saturating transformer or reactor T.Tothesecondary. winding of said'satm'ating transformer are connected apair of gas rectifying, tubes. N21 and N22. To said gas tubes are also.connected the windings of short-circuiting relays. R10. and R20, onlytwo of which are shown. Theremaining terminals. of the windings of saidrelays R1u.and.R2o are connected to the midpoint of the. secondary ofthe saturating transformer T or. to said. transformer terminal in serieswith a source of biasing potential B, as shown. The biasing potential.should at all times be less than the. voltage required to sustain theglow within the. gas. tubes, otherwise the tubes when once operatedwouldlock said short-circuiting relays R10 and. Rain. the operated position.

The short-circuiting relays each have two windingsin order thatthere besome ballast resistance in thecircuitv connected between the cathodes ofthe rectifying tubes. Gas tubes do not totally blockcurrents when poledin the reverse direction with respect to the alternating current cycleand the introduction of impedance to the flow of current in-the reversedirection is required to prevent. damage to the gas tubes.

Operation. in. Fig. l isv as follows: Voltage applied to any one or allconductors W1 to W4 inclusive of suflicient amplitude to cause thebreakdown of any one of the protector blocks P1 to P4 inclusive resultsin the passage of current through the primary winding of the transformerT. This current introduces a potential in the secondary winding of saidtransformer and if of sufficient amplitude will cause current to passfrom the anodes (designed by the arrows) to the cathodes or the gastubes N21 and N22 and thence through the windings of theshort-circuiting relays R10 and R associated therewith and thence to themidpoint: of' thesecondary winding of the transformer '1 through thesource of biasing potential, if such asource is present and employed inthe system. If the potential at l of the transformer T is positive andat 2 negative, the gas tubeNzi will function and allow current to flowthrough the left-hand winding of relays R10 and R20. If, however, thepolarity is reversed, the gas tube N22 will'function and allow currentto flow through the right-hand windings of relays Rio andRm. Thepassageof current through either of the windings of relays R10 and R20causes the armatures to be attracted to their contacts,resulting-in'thesimultaneous short-circuiting of the protector blocks P1to P4, respectively. Current from the conductors to earth will continueto pass through the transformer T and the short-circuit ingrelaysassociated with said transformer will be held operated until thedisappearance of the applied potential or until it has dropped to avalue less than that required to sustain the glow within the gas tubes.

In Fig. 2 full wave. rectification is also obtained. by utilizing fourgas rectifying tubes of the cold'cathode type. If the potential ispositive at I, current will pass through the gas tube N23 and throughthe left-hand windings of the short-circuiting relays R30. and R40associated therewith to the gas tube N24 and returning to thetransformer at 2. For a potential of opposite polarity, current willpass through the gas tube N25 to the right-hand windings of theshortcircuiting relays R and R associated therewith and-thence throughgas tube N20 and returning to the transformer at I.

It will be understood that the individual shortcircuiting relays canbereplaced by a single shortcircuiting relay having a multiplicity ofarmatures and contacts, said individual relay containing two windings,provided the gas tubes can pass current in the inverse position of thealternating current wave. Where cold cathode gas tubes can be designedto pass current in but one direction,.a single wound relay need only beemployed. It will be furthermore understood that the gas tubes of thecold cathode type may be replaced by gas tubes of the hot cathode type,in which case but a single winding will be required on theshort-circuiting relays, as will be apparent to those skilled in thisart. It will be furthermore understood that a condenser C or condensersC may, if desired, be used to shunt the windings of the relays toprevent chatter of said relays by supplying current during the period inthe alternating current cycle when there is no current being passed bythe gas tube rectifiers.

While this invention has been described and shown in said particulararrangements merely for the purpose of illustration it will beunderstood that the general principles may be applied to other andwidely varied organizations without departing from the spirit of theinvention and the scope of the appended claims.

What is claimed is:

1. Apparatus for the protection of a plurality of circuits exposed toinductive interference comprising a plurality of protector blocks oneterminal of each of which is connected to a correspond ing circuit, atransformer the primary winding of which is connected between the otherterminal of each of said protector blocks and ground, two two-electrodecold cathode gas-filled rectifier tubes, a relay having two windingseach of which is connected in series with one of said tubes and one-halfof the secondary winding of said transformer, and means responsive tothe operation of said relay for simultaneously shunting all of saidprotector blocks.

2. Apparatus for the protection of a plurality of circuits exposed toinductive interference comprising a plurality of protector blocks oneterminal of each of which is connected to a corresponding circuit, atransformer the primary winding of which is connected between the otherterminal of each of said protector blocks and ground, two two-electrodecold cathode gasfilled rectifier tubes, a biasing battery having aterminal voltage which is less than the voltage for sustainingionization with said tubes, a relay having two windings each of which isconnected 10 in series with one of said tubes and the biasing batteryand one-half of the secondary winding of said transformer, and meansresponsive to the operation of said relay for simultaneously shuntingall of said protector blocks.

LELAND KASSON SWART.

